In the context of increasing genetic variation within a population of earthworms, the activity that achieves this is sexual reproduction. Here's a breakdown of why sexual reproduction is the correct answer:
1. **Sexual Reproduction**: In sexual reproduction, genetic material from two parents is combined to create offspring with a unique genetic makeup. This process introduces new genetic combinations and variations within the population, promoting genetic diversity.
2. **Binary Fission**: Binary fission is a form of asexual reproduction where an organism duplicates its genetic material and divides into two identical individuals. This process does not contribute to genetic variation as there is no exchange of genetic material between different individuals.
3. **Budding**: Budding is another form of asexual reproduction where an offspring develops as a growth on the parent organism. Similar to binary fission, budding does not involve the mixing of genetic material from different individuals, thus limiting genetic diversity.
4. **Fragmentation**: Fragmentation is a method of asexual reproduction where an organism breaks into fragments, each of which can grow into a new individual. Like binary fission and budding, fragmentation does not involve genetic recombination from different sources, therefore not contributing to genetic variation.
Therefore, in the case of earthworms, sexual reproduction is the activity that increases genetic variation within the population by combining genetic material from two different parents to produce offspring with diverse genetic traits.
